The disclosure of Japanese Patent Application No. 2001-129725 filed on Apr. 26, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to control systems and methods of an internal combustion engine, for controlling opening and closing of an intake flow control valve disposed downstream of a throttle valve in an intake pipe, depending upon an operating state of the engine.
2. Description of Related Art
An intake control system of an internal combustion engine is known which controls opening and closing of an intake flow control valve disposed downstream of a throttle valve within an intake pipe, depending upon an operating state of the engine. The intake control system of this type operates to close the intake flow control valve, for example, upon a start of the engine with a light load, to thus reduce an effective cross-sectional area of a portion of the intake pipe in which the control valve is mounted, thereby restricting flow of intake air through that portion of the intake pipe. With this control, the flow velocity of the intake air passing downstream of the intake flow control valve is increased, and the magnitude of a negative pressure as measured in the intake pipe downstream of the valve is increased. As a result, atomization of fuel that is injected into the intake pipe by an injector disposed downstream of the intake flow control valve is promoted, and turbulence is created in a combustion chamber, thus leading to an improvement of combustion characteristics of the engine.
An intake control system as disclosed in Japanese laid-open Patent Publication No. 10-141126 is operable to detect an abnormality or failure in the intake flow control valve that is placed in the open or closed position, and to perform fail-safe control of the internal combustion engine by controlling the fuel injection amount and the injection timing upon detection of an abnormality in the intake flow control valve. However, the control system is not arranged to control the intake flow amount or flow rate in such a situation.
It is therefore one object of the invention to provide a control system of an internal combustion engine, which controls the intake air amount or flow rate upon detection of an abnormality in the open or closed position of an intake flow control valve, so as to stabilize combustion of an air-fuel mixture in a combustion chamber.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention, a control system of an internal combustion engine including an intake flow control valve disposed downstream of a throttle valve, comprising a controller that (1) controls opening and closing of the intake flow control valve, depending upon an operating state of the internal combustion engine, (2) detects a failure of the intake flow control valve that is placed in an open position when control for closing the intake flow control valve is performed, and (3) controls an intake air amount to an increased value when the failure is detected, so as to stabilize combustion of an air-fuel mixture in the engine.
In the internal combustion engine equipped with the intake flow control valve, the intake air amount during idling and the fuel injection amount at the time of a cold start of the engine are normally set to smaller values than those for an engine having no intake flow control valve, and the air/fuel ratio of an air-fuel mixture to be burned is set to be on the lean side, in view of an effect of improving combustion characteristics through an operation of the intake flow control valve. If the intake flow control valve is placed in the open position due to a failure, therefore, the intake air amount during idling becomes insufficient, and needs to be increased. According to the above aspect of the invention, the intake air amount is controlled to an increased value upon a failure of the intake flow control valve, thus assuring a sufficiently high idling speed and stabilized combustion.
It is preferable to increase a fuel injection amount and/or advance an injection timing, as well as increasing the intake air amount, when the intake flow control valve is placed in an open position due to a failure.
According to another aspect of the invention, there is provided a control system of an internal combustion engine including an intake flow control valve disposed downstream of a throttle valve, comprising a controller that (1) controls opening and closing of the intake flow control valve, depending upon an operating state of the internal combustion engine, (2) detects whether the intake flow control valve is sticking at a certain opening angle, and (3) when detecting sticking of the intake flow control valve, controls opening and closing of the throttle valve in accordance with a degree of sticking of the intake flow control valve.
When the intake flow control valve is stuck at a certain position or opening angle, flow of intake air through the intake pipe is restricted by the intake flow control valve, and it becomes difficult to insure that a sufficiently large amount of intake air is supplied to the combustion chamber. According to the above aspect of the invention, therefore, opening and closing of the throttle valve is controlled so as to ensure a sufficiently large amount of intake air.
Here, it is preferable to correct an opening angle of the throttle valve in relation to an amount of depression of an accelerator pedal, in accordance with the degree of sticking of the intake flow control valve.